1. Field of the Invention
The present invention relates to a process for separating, or isolating, at least two fractions each enriched with a component from a fluid containing a plurality of useful components, and particularly relates to a process for separating a plurality of components contained in a gas or liquid containing at least two or three components according to a chromatographic procedure.
2. Prior Art
Processes for separating a Plurality of components according to a chromatographic procedure (hereinafter referred to as a chromatographic separation process have heretofore been widely utilized on an industrial scale.
For example, many packed bed units 1 to 8, as shown in FIG. 4, packed with a solid adsorbent are connected in a series of circulation to establish a chromatographic system. The so-called simulated moving bed process involves feeding of a fluid feed f, a liquid in particular, to the above-mentioned system from the outside of the system, feeding of an eluant D as the desorbing fluid to the system from the outside of the system, withdrawal of fractioned components A and B from the system to the outside of the system, circulation of an internal liquid by means of a circulation pump, switching of valves 1a to 8a, 1b to 8b, 1d to 8d and 1e to 8e to simulate a moving bed to thereby continuously separate the components A and B. This simulated moving bed process is known as being excellent in separation performance and high in productivity to make the process as well as equipment therefor advantageous.
The simulated moving bed process as briefly described above is required to have feeding inlets for a fluid feed and feeding inlets for a desorbing fluid (hereinafter referred to as a fluid desorbent ) between adjacent packed bed units, and withdrawal outlets for withdrawing fractions of components to be withdrawn. Accordingly, not only simulation of a moving bed without actual movement of an adsorbent is difficult to understand in an aspect of principle, but also adoption of a complicated structure of whole equipment as described above is difficult to avoid in another aspect. Thus, as compared with equipment for a batch operation, which equipment can realize separation of components from a mixture thereof by a relatively simple operation, continuously operable equipment requires a high degree of control technology. Accordingly, such continuously operable equipment is known to bear an onus, or burden, of an overall equipment cost in aspects of both hardware and software.
Furthermore, a simulated moving bed mode of processes has heretofore been, in general, used to fractionate components contained in a gas or liquid into two fractions. Thus, it has heretofore been considered difficult to fractionate a fluid containing at least three components into at least three fractions.
The inventors of the present invention have already proposed a method capable of separating at least three components without spoiling the excellent separability performance of the simulated moving bed mode by improving on the conventional technology of the simulated moving bed, which has heretofore been considered as being aimed at two, or twin, component systems as an object of separation.
Specifically, Japanese Patent Application No. 402,826/1990, which was proposed by the inventors of the present invention, discloses a process for fractional separation of a fluid mixture comprising a number of components into three or more components, which process is carried out in a system wherein a number of bed units packed with an adsorbent are linked with each other in endless, or continuous, series in such a way as to form a circulatory channel capable of circulation and shutoff, and wherein a fluid feed, or mixture, comprising three or more components having mutually different affinities for the adsorbent is flowed through said number of the packed bed units to form adsorption zones of the respective components separated from each other in the serial order of the weak to strong affinities thereof for the adsorbent; and which process comprises repeating a cycle comprising the step (1) of shutting off fluid circulation of said system at the shut-off position and feeding the fresh fluid feed into the system at a position downstream of the shutoff position while withdrawing from the system a fraction enriched with a component having an intermediate affinity for the adsorbent (predetermined component) selected from components present in adsorption zones located upstream of the shut-off position; and the step (2) of separately withdrawing enriched fractions of the respective components from the adsorption zones from which the predetermined component has not been withdrawn in the step (1) by feeding a fluid desorbent into the system from the upstream side of the adsorption zones with sequentially shifting the position of feeding the fluid desorbent and the positions of withdrawing enriched fractions, corresponding to the migration of the respective adsorption zones, in the downstream direction of circulation, while circulating the internal fluid throughout the system and feeding no fresh fluid feed into the system.
By the way, one characteristic of the above-proposed process is having the step of feeding the fluid feed while shutting off at least one position of the circulation system. The authors of the present invention have further found out that utilization of this characteristic step enables the following multi-component system separation operation.
Specifically,
(1) the utilization of the step of feeding the fluid feed while shutting off fluid circulation at the shut-off position enables a fluid feed containing two components as an object to be subjected to the prior art simulated moving bed procedure to be more effectively fractioned into the respective fractions; and
(2) in the step (2) of the above-proposed prior art process, the position from which the fluid desorbent is fed upstream of the adsorption zone enriched with a predetermined component while circulating the internal fluid by means of a pump or the like, the position from which the fraction enriched with the component having a strong affinity for the adsorbent is withdrawn, and the position from which the fraction enriched with the component having a weak affinity for the adsorbent is withdrawn, must be shifted in step with the migration of the adsorption zones of the respective components while sequentially shifting downstream the feeding inlet of the first-mentioned position and withdrawal outlets of the second- and third-mentioned postions, whereby sequence control as well as the structure of equipment tends to be complicated. Thus, a further improvement is demanded in simplification of the sequence control as well as the structure of equipment.
In view of the above, the present invention has been completed. Accordingly, an object of the present invention is to provide a novel process and equipment therefor which enable a mixture containing two or more components, two components in particular, to be effectively fractioned into fractions enriched with the respective components.
Another object of the present invention is to provide a process according to which separation, or fractionation, of three or more fractions, which has heretofore been impossible using the prior art twin-component simulated moving bed equipment, can be carried out using by far simpler simulated moving bed equipment than the prior art simulated moving bed equipment.